Chemical treatment for silica-containing glass surfaces

ABSTRACT

Dehydroxylated, silica-containing, glass surfaces are known to be at least partially terminated by strained siloxane rings. According to the invention, a surface of this kind is exposed to a selected silane compound or mixture of silane compounds under reaction-promoting conditions. The ensuing reaction results in opening of the strained siloxane rings, and termination of surface atoms by chemical species, such as organic or organosilicon species, having desirable properties. These species can be chosen to provide qualities such as hydrophobicity, or improved coupling to a polymeric coating.

GOVERNMENT CONTRACT

This invention was made with Government support under Funds-In AgreementNo. DE-FI04-88AL54100, awarded by The United States Department ofEnergy. The government has certain rights in this invention.

This is a continuing application Ser. No. 08/261,565, filed Jun. 17,1994, now U.S. Pat. No. 5,736,245.

FILED OF THE INVENTION

The invention relates to surface treatments for silica-containing glass,and in particular, to treatments for the purpose of suppressingcorrosion of the glass surface by moisture, and treatments for thepurpose of promoting adhesion to a polymeric coating. In a specificembodiment, the invention relates to such surface treatments in themanufacture of polymer-clad fiber-optic cables.

ART BACKGROUND

A freshly formed, silica-containing, glass surface will include adistribution of reactive sites that may include structural surfacedefects. It is well known that atmospheric moisture will react withthese sites, leading to the attachment of hydroxyl groups to siliconatoms. As a result, a glass surface that has been exposed to the ambientatmosphere for a substantial period of time may be described as a"silanol-terminated" surface.

It is conventional to use silane coupling agents, such as RSi(OMe)₃ inthe example below, to improve the adhesion of polymers to asilanol-terminated surface. Thus, for example, the water-mediatedreactions:

    RSi(OMe).sub.3 +H.sub.2 O+HOSi.tbd.→MeOH+[RSi(OMe).sub.2 ]OSi.tbd.+H.sub.2 O

    2[RSi(OMe).sub.2 ]OSi.tbd.+H.sub.2 O→2MeOH+.tbd.SiO[R(OMe)]SiOSi[R(OMe)]OSi.tbd.

provide a cross-linked siloxane surface that contains covalent couplingpoints R for a subsequent organic reaction with a polymer.

Such reactions may be useful for promoting the adhesion of an opticalfiber to a polymeric jacket material. Even absent such jacket material,reactions of this kind may be useful for attaching chemical species tothe glass surface that are effective for reducing the affinity of thesurface, or of the glass-polymer interface, to water. For both of thesereasons, a surface reaction of this kind may be able to impart desirableproperties to glass fibers for use, e.g., in fiber-optic cables.

However, a surface treatment that relies upon the availability of asilanol-terminated surface will not, in general, be the most economicalor effective treatment to use in optical fiber manufacture. This isbecause in large-scale fiber-making operations, the application of thepolymeric coating is typically integrated in a continuous process thatbegins with drawing of fresh fiber from a heated preform, and ends withwinding the coated fiber on a spool. The freshly drawn glass will nothave a silanol-terminated surface. Instead, it will have a nearlydehydroxylated surface that is partially terminated by strained andunstrained siloxane rings.

In fact, there are known surface reactions that can attach organicspecies directly to a dehydroxylated glass surface. These reactions aredescribed, for example, in L. H. DuBois et al., J. Amer. Chem. Soc. 115(1993) 1190-1191, and L. H. DuBois et al., J. Phys. Chem. 97 (1993)1665-1670. As discussed there, an alkoxy silane can react directly witha type of surface defect referred to as a "strained siloxane dimerring," or, in reference to its geometrical configuration, as an"edge-shared tetrahedral defect" However, the resulting surface productcontains a hydrolyzable alkoxy ester. This is undesirable because it mayprovide a nucleation site for the condensation of water. This, in turn,can weaken an optical fiber by way of a stress-induced corrosionmechanism. Moreover, the alkoxy ester is undesirable as a coupling pointbetween the glass surface and a polymeric coating, because the adhesivebond to the polymer will be hydrolytically unstable. The surfacereaction and subsequent hydrolysis are illustrated in FIG. 1.

Thus, practitioners in this field have hitherto failed to provide aneffective chemical treatment for dehydroxylated glass surfaces, thataffords protection fr6m moisture and can promote adhesion to polymericcoatings.

SUMMARY OF THE INVENTION

A desirable reactant, for the purposes described above, would produce asurface which is terminated by desirable coupling or passivatingchemical groups. These chemical groups will typically be chosen to beintrinsically hydrolytically stable, or hydrolytically stable after asubsequent reaction with an organic compound (such as a polymer). Wehave discovered that certain silane compounds are readily used toachieve this result They are those compounds of silicon that have atleast one Si--H group and/or at least one Si--O--Si group.

The reaction should be carried out such that: oxygen atoms belonging tothe glass surface form chemical bonds with silicon atoms of the siliconcompound; silicon atoms belonging to the surface form chemical bondswith hydrogen or oxygen atoms of the silicon compound; and the chemicalreaction results in no net increase in the number of O--H bonds at thesurface. (In many cases, in fact, it will be possible to carry out thereaction such that no new O--H bonds are formed.) Because alkoxysilanestend to be hydrolytically unstable, the reaction should further becarried out such that no oxygen atom is simultaneously bound to asilicon atom and a carbon atom in any product of the reaction.

Included in the class of useful compounds are: silane; the siloxanes andtheir analogs; the cyclosiloxanes and their analogs; theorgano-H-silanes and their analogs, and the organosiloxanes and theiranalogs.

In these reactions, the strained dimer ring is opened by the breaking ofa Si--O bond. A new bond is made between the exposed oxygen atom and asilicon atom of a silane species (which may be a siloxane,organo-H-silane, or organosiloxane species). A new bond is made betweenthe exposed silicon atom and either a hydrogen atom, or an oxygen atomof a siloxane species (which may be an organosiloxane species).

Significantly, these reactions conserve the number and kinds of bonds inthe reacting molecules. Consequently, the driving force for the reactionis provided substantially by the release of the ring strain at thesurface site. We have found that, surprisingly, the reaction kineticsare rapid enough to provide a practical method for functionalizing adehydroxylated surface of silica-containing glass, such as ahigh-temperature formed silica surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents, using structural formulas, surface reactions of theprior art in which an organic species is attached to a glass surface andsubsequently hydrolyzed.

FIGS. 2 and 3 represent strained dimer rings that are present atdehydroxylated surfaces of silica-containing glass.

FIGS. 4 and 5 represent alternative surface reactions according to theinvention in some embodiments.

FIG. 6 represents a general photocatalyzed reaction between a glasssurface and a vinylated species.

FIG. 7 schematically represents a method for making fiber-optic cableaccording to the invention in one embodiment.

FIG. 8 schematically represents a method for modifying the surfaces offumed silica particles, according to the invention in one embodiment.

FIGS. 9 and 10 represent, using structural formulas, chemical reactionsinvolving siloxane rings at glass surfaces.

FIG. 11 is an experimental plot showing the extent of reaction, as afunction of dose, for reactions between a glass surface and water andbetween a glass surface and each of four exemplary silane compounds.

DETAILED DESCRIPTION

From infrared spectroscopic evidence, we have estimated that straineddimer rings cover about 2%-3% of the dehydroxylated surface. This isequivalent to 0.2-0.4 reactive sites per nm². These rings may exist inseveral forms, the two most likely of which are shown in FIG. 2 (theso-called d₄ form) and FIG. 3 (the so-called d₃ form). (See, e.g., T. A.Michalske et al., J. Appl. Phys. 56 (1984) 2686, and B. C. Bunker etal., Surf. Sci. 222 (1989) 95-118.) We have found that the d₄ form isthe more reactive of these, and that this form accounts for at least 25%of all the strained ring sites.

Hereinafter, a glass surface will be referred to as "siloxaneterminated" if it has at least about 0.005 strained dimer rings per nm².

An exemplary reaction, according to the invention, is shown in FIG. 4.Here, a generic siloxane compound R₁ R₂ R₃ Si--O--SiR₄ R₅ R₆ is reactedwith a strained dimer ring ═Si(O₂)Si═. In this representation, each ofthe symbols R₁ -R₆ represents (subject to certain constraints) anyspecies selected from hydrogen atoms, organic species and their analogs,silane species and their analogs, organosilane species and theiranalogs, and organosiloxy species and their analogs. As noted, however,alkoxysilanes are generally undesirable as reactive compounds, due tohydrolytically unstable end products that would be produced on thesurface. In some cases, chlorosilanes, silazanes, and silamines may alsobe undesirable for similar reasons.

In each radical R, the atom bonded directly to the corresponding siliconatom of the .tbd.Si--O--Si.tbd. structure must be either hydrogen,carbon, or oxygen.

An alternative reaction is shown in FIG. 5. Here, the dimer ring isreacted with SiH₄ or a derivative thereof. This reaction results in thehydrogenation of the exposed dimer silicon atom. With respect to theexposed dimer oxygen, this reaction is similar to the reaction of FIG.4.

In regard to either type of reaction, it is well known that theunstrained SiOSi structure produced by the ring opening is far lesssusceptible to hydrolysis than are the alkoxy esters.

One terminal group that is readily produced by either of these types ofreaction is the group .tbd.SiH. This is one of many groups that cancouple a polymeric coating to the glass surface. For example, FIG. 6illustrates a photocatalyzed reaction between .tbd.SiH and a vinylatedspecies H₂ C═CH--R. This reaction is described in W. Noll, Chemistry andTechnology of Silicones, Academic Press, New York, 1968. The actinicradiation for catalyzing this reaction can, in at least some cases, beprovided by the same light source used to photocure the polymericcoating. This is convenient where, for example, the polymeric coating isapplied to optical fiber in a continuous process integrated with thedrawing of the fiber.

A partial list of the silane (including siloxane) compounds that can beused to terminate dehydroxylated glass surfaces appears in the Appendix.Currently preferred compounds are: hexamethyldisiloxane (hMdS), 1,1,3,3tetraMethyldiSiloxane (tMdS), 1,1,3,3 tetraVinyldiMethyldiSiloxane, 1,3di(3-AminoPropyl)diMethyldiSiloxane, 1,3di(3-MercaptoPropyl)diMethyldiSiloxane, the MethylHydrocycloSiloxanes,hexaMethylcyclotriSiloxane (hMctS), isomers oftri(MethylHydro)cyclotriSiloxane, pentaMethylcyclotriSiloxane,EthylSilane (EtS), diMethylsilane, and the (MethylHydro)polySiloxanes.

Among these compounds, we found that tMdS, in particular, reacts quicklyenough to be used in the processing of optical fiber. As discussedbelow, we reacted this compound with dehydroxylated silica particleshaving a surface area of about 200 m² g. We found that at a surfacetemperature of about 480° K., the surface reaction was substantiallycomplete after about one second in the presence of tMdS vapor at 200torr of pressure. (The vapor pressure of this chemical is 200 torr at30° C.) The total exposure is the integral of the reactive vaporpressure as a function of time. Thus, in this case, the exposure wasabout 200 torr-s. Because we believe that this dose caused more than 99%of the strained dimer rings to react, we estimate that this treatmentwill provide about 0.3 covalent coupling points per nm² of surface area.(In general, a reaction more than 90% complete will be considered"substantially complete.") For processing optical fibers or otherglass-comprising articles, it will generally be desirable to perform thereactive exposure before the article has come into contact with asubstantial dose of water vapor. By "substantial dose" is meantsufficient exposure to impair the useful properties imparted by theinventive surface treatment. Thus in typical cases, it will be desirableto avoid any exposure to water vapor, prior to the desired reactiveexposure, that would result in terminating more than about 10% of theavailable reactive sites with OH.

In an exemplary fiber production operation, as depicted schematically inFIG. 7, a reaction zone 10, exemplarily one meter long, can be added toa fiber draw tower. Within the reaction zone, a controlled atmospherefrom source 20 is maintained about the unfinished cable. In this zone,fiber 30, freshly drawn from preform 40 in furnace 50, will pass throughgas-phase reactor 60. Heat will be provided either as residual heat inthe fiber, or from heat sources associated with the reactor. The fiberwill pass through the reactor at a speed in the range 1-100 m/s (speedsof about 10 m/s are typical). The fiber speed, surface temperature, andreactant vapor pressure will be adjusted such that the surface reactionis substantially completed during passage through the reaction zone. Thesurface-modified fiber will then pass to processing station 70 and 80for respectively applying and curing the polymer coating. Thepolymer-coated fiber is then wound on capstan 90. It is expected that bythis means, improved moisture resistance can be imparted to opticalcable with only a modest increase in production cost.

In at least some cases, it may be desirable to use this surfacemodification to control the degree of adhesion between the fiber surfaceand the polymeric coating. That is, if the adhesion is too weak,debonding may occur, which causes optical attenuation losses in thefiber due to a microbending mechanism. On the other hand, if adhesion istoo strong, it is difficult for workers to strip the ends of opticalcables to prepare them for splicing or installation. A mixture ofchemicals can be selected, which includes a relatively strong adhesionpromoter, diluted with a second chemical (and possibly others) that iseffective for passivating the glass surface, but contributes relativelyweak adhesion, if any, to the polymeric coating.

One example of such a mixture is a 1:1 (with respect to gas-phasedensity) mixture of hMctS and tMdS. These two chemicals react at nearlyidentical rates, but the contribution of hMctS to the adhesion isnegligible relative to that of tMdS. As a consequence, this mixture willlead to about half the adhesion produced by tMdS alone.

Another useful application of the inventive surface treatment is for thein situ modification of fumed silica surfaces for use as, e.g., a fillermaterial. For example, it is well known that fumed silica particles canbe made in, and ejected from, a tetrachlorosilane burner. As depictedschematically in FIG. 8, the outlet 120 of such a burner 110 will bereadily attached to the inlet of a reactor 130, such as a gas-phasereactor, containing a controlled atmosphere comprising vapors oraerosols of appropriate silane compounds. The temperature and reactivevapor pressure (or equivalent pressure in the case of aerosols) in thereactor will be adjusted to substantially complete the desired surfacereaction within an appropriate residence time, exemplarily 0.5 s. Duringthis residence time, the fumed silica 140 will pass through the reactorand into a bagging outlet 150, similar to the bagging outlets ofconventional burners for fumed silica production. We expect that themodified silica that results from this process will exhibit improvedmoisture resistance relative to conventional fumed silica products, andwill in at least some cases exhibit improved adhesion to the surroundingmatrix material, resulting in better mechanical stability. We believethat this can be achieved with only modest modification of conventionalplant equipment.

Yet another useful application of the inventive surface treatment is forpassivating silicon dioxide surface layers on silicon substrates. Forexample, several steps in the manufacture of silicon integrated circuitsinclude the formation of a silicon dioxide surface layer on a siliconwafer. This layer may be formed, in some cases, by in situ oxidation,and in other cases by a deposition process. In either case, it is oftendesirable to protect such a layer from corrosion by moisture.

Another kind of device formed on a silicon substrate is a planar glasswaveguide, which comprises numerous silica-containing layers. It willoften be desirable to protect at least certain of these layers, such asthe uppermost layer, from corrosion by moisture.

Silicon micromachines are yet a third kind of device which may beimproved by a chemical surface treatment. In these devices, a nativesilicon dioxide surface layer is generally present It will often bedesirable to treat these surfaces to provide a stable, low frictioninterface between moving parts, and to protect the device from moisture.

We believe that our surface treatment will be useful for the protectionof devices of these illustrative kinds. An appropriate silane chemical(or mixture of chemicals) may be applied to the wafer (or other siliconsubstrate) surface in a gas-phase reactor. Alternatively, a liquidsilane chemical (or mixture) may be applied. (In the case of flatsubstrates, spinning may be an appropriate liquid-application process.)As yet another alternative, a low-vapor-pressure silane or mixture maybe applied in the form of an aerosol. Appropriate sources of heat forpromoting the surface reaction will be well known to practitioners inthe art of semiconductor fabrication, and need not be described indetail.

In regard to the cyclic compound hMctS, we have found evidence ofsurface-catalyzed polymerization. That is, at the dehydroxylated glasssurface, strained dimer rings can open and fuse with a molecule ofhMctS. This leads to an even larger ring, pinned to the reactive surfacesite. This reaction is illustrated in FIG. 9.

We believe that additional, unreacted molecules of hMctS will fuse withthe pinned rings of FIG. 9, to produce even larger pinned rings.Adhesion of a polymeric coating to a surface treated in this manner willbe enhanced by entanglement of the pinned rings with the polymer chains.We further believe that unstrained siloxane rings even larger than hMctS(such as the next larger analog, octarnethyl cyclotetrasiloxane) willreact with the strained dimer rings in a similar way. These largercyclic compounds will also be useful for promoting adhesion.

We have observed that hMctS will react, not only with the strained dimerrings, but also with residual hydroxyl groups attached to the silicasurface. The reaction opens the hMctS ring to form a straight chainbonded to .tbd.Si--O-- at the surface and terminated by --Si--OH. Two ofthese terminal --Si--OH groups may condense, with the loss of a watermolecule, to produce a doubly pinned, fused ring. These reactions areillustrated in FIG. 10. We have observed the trisiloxane ring-openingreaction even on silica surfaces that were treated with water tore-hydroxylate them.

In the hMctS ring-opening reaction, a new O--H bond is formed, but thereis no net increase in the number of O--H bonds at the glass surface.

EXAMPLE

We reacted water, EtS, tMdS, hMdS, and hMctS with high-surface-areasilica obtained from the Cabot Corporation of Tuscola, Ill. This silicahas a surface area of ##EQU1## and a structure composed of aggregates ofdense ;spherical particles having a 7-nm mean particle radius.

The reactions were carried out in a turbo-pumped stainless steel vacuumchamber having a base pressure of 10⁻⁸ torr. The reactions were carriedout at 480° K. This temperature was selected because it led to ameasurable reaction rate for all of the chemicals we wished to observe,but was not high enough to cause pyrolysis of the reaction products.

Samples were prepared by depositing about 1.5-2 mg of silica in acolloidal suspension in methanol as a central stripe on a tungsten meshcovering an area of 1 cm². The mean sample thickness was about 8 μm. Thesamples were cleaned in situ by heating in the presence of oxygen at500° C.

Prior to any surface reaction, the samples were heated in vacuo at 1050°C.-1100° C. for one hour, and then rapidly quenched to the reactiontemperature of 480° K. This heating step brought the samples to thestrain point for silica (approximately 1100° C., depending on theimpurity level). Because viscous flow can occur at this temperature, webelieve that the subsequent quenching step captured defects and theirimmediate surroundings in their high-temperature form.

Before performing the surface reactions, we took infrared spectra of thesamples. Signature absorption peaks at 882 cm⁻¹ and 902 cm⁻¹ indicatedthe presence of strained dimer rings. Each sample was briefly (i.e., for50-200 s) exposed to the reactant The sample was then pumped free ofreactant, and another infrared spectrum was taken. This sequence wascycled with exponentially increasing gas pressures, such that thecomplete set of exposures spanned six orders of magnitude of total dose.

FIG. 11 shows the extent of the surface reaction as a function of dose.The extents of the reactions with water and hMctS were measured by theattenuation of the infrared absorption peaks at 882 cm⁻¹ and 902 cm⁻¹.However, in the other cases, these absorption peaks were masked by thegrowth of interfering bands due to infrared absorption by certainfunctional groups on the reacting silanes. In these cases, we usedinfrared spectroscopic evidence of the growth of material on the surfaceto infer the degree to which defects were lost.

It is evident from the figure that a dose of about 200 torr-s produced asubstantially complete reaction with water, hMctS, and tMdS.

We estimated that EtS reacts with dimer rings about 2200 times moreslowly than tMdS, and it does not appear to react with surface hydroxylgroups at doses less than 6×10⁴ torr-s. We estimated that hMdS reactsabout 600 times more slowly than tMdS, and it does not appear to reactwith surface hydroxyl groups. It is evident from the figure that hMctSreacts at a rate slightly faster than that of tMdS.

As noted above, we believe we have found evidence of a hMctSpolymerization reaction, and of reactivity of hMctS with residualsurface hydroxyl groups. We have also noted that at 480° K., but not at350° K., a polymerization reaction appears to take place between SiH atthe surface and the Si--O bonds of gas-phase molecules of tMdS.

Significantly, the kinetic data displayed in FIG. 11 will be useful forestimating the exposures needed to obtain substantially complete surfacereactions with a broad range of reactive compounds. That is, thereactive center of each of the compounds listed in the Appendix has thesiloxane structure Si--O--Si or (in the case of the SiH₄ derivatives)the organo-H-silane structure Si--H. Neglecting, for now, the effect ofsteric hindrance, the tMdS reaction is expected to typify the rates tobe expected with the first of these structures, and the EtS reaction isexpected to typify those rates expected with the second structure. Asnoted, hMdS reacts more slowly than tMdS. We attribute this primarily tosteric hindrance. Because hMdS is a highly hindered molecule, we believethat the hMdS reaction typifies the slowest rates, associated with themost hindered siloxane compounds that will have useful application inthe practice of our invention. Accordingly, we expect effective totalexposure values to span a range of about three orders of magnitude fromsiloxane compounds to comparably hindered organo-H-silane compounds, andto span a range of about three orders of magnitude from minimallyhindered to highly hindered, compounds of either class.

In addition to the four compounds discussed above, we measured reactionrates between silica and the compounds: tris-triMethylSiloxySilane;1,1,3,3-tetraMethyldiSilazane; 1,3-diVinyltetraMethyldiSilazane;VinyldiMethylEthoxySilane; and tetraEthylSilane. The reactivities ofthese compounds were roughly as would be expected from the abovediscussion. As a group, these reactivities spanned a range of about sixorders of magnitude.

APPENDIX

(Note: As used herein, "HydroSiloxane" denotes a siloxane that containsthe SiH group.)

A. hexaMethyldiSiloxane and its derivatives:

hexaMethyldiSiloxane

1,1,3,3 tetraMethyldiSiloxane

1,1,3,3 tetraVinyldiMethyldiSiloxane

1,3 di(3-AminoPropyl)diMethyldiSiloxane

1,3 di(3-MercaptoPropyl)diMethyldiSiloxane

1,3 diBenzyltetraMethyldiSiloxane

1,3 diPhenyl 1,1,3,3 tetrakis(diMethylSiloxy)diSiloxane

1,3 diPhenyltetraMethyldiSiloxane

1,3 diVinyl 1,3 diPhenyl 1,3 diMethyldiSiloxane

1,3 diVinyl tetraMethyldiSiloxane

hexaEthyldiSiloxane

tris-(triMethylSiloxy)Silane

B. CycloSiloxane Derivatives:

the MethylHydrocycloSiloxanes

hexaMethylcyclotriSiloxane

isomers of tri(MethylHydro)cyclotriSiloxane

pentaMethylcyclotriSiloxane

1,3,5,7 tetraVinyltetraMethylcyclotetraSiloxane

hexaEthylcyclotriSiloxane

C. Derivatives of Silane (SiH₄)

EthylSilane

diMethylsilane

diEthylSilane

diEthylMethylSilane

D. Derivatives and Oligomers of polydiMethylSiloxane

the (MethylHydro)polySiloxanes

1,1,3,3,5 hexaMethyltriSiloxane

We claim:
 1. A method, comprising the steps of:providing an article comprising silica-containing glass, said glass having a siloxane-terminated surface; and exposing the surface to a compound of silicon having at least one Si--H group and/or at least one Si--O--Si group, resulting in a chemical reaction between the surface and said silicon compound, wherein the exposing step is carried out such that:a) oxygen atoms belonging to the surface form chemical bonds with silicon atoms of the silicon compound; b) silicon atoms belonging to the surface form chemical bonds with hydrogen or oxygen atoms of the silicon compound; c) no oxygen atom is simultaneously bound to a silicon atom and a carbon atom in any product of the chemical reaction; and d) the chemical reaction results in no net increase in the number of O--H bonds at the surface.
 2. The method of claim 1, wherein the silicon compound is selected from the group consisting of: SiH₄, the siloxanes and their analogs, the cyclosiloxanes and their analogs, the organo-H-silanes and their analogs, and the organosiloxanes and their analogs.
 3. The method of claim 2, wherein the silicon compound does not belong to the group consisting of: the alkoxysilanes and their analogs, the chlorosilanes and their analogs, the silazanes and their analogs, and the silamines and their analogs.
 4. The method of claim 1, wherein the silicon compound is a siloxane compound that may be represented by the general formula R₁ R₂ R₃ Si--O--Si R₄ R₅ R₆ wherein:a) each of the symbols R₁ -R ₆ represents a substitutional species selected from the group consisting of: the hydrogen atom, the organic species and their analogs, the silane species and their analogs, the organosilane species and their analogs, and the organosiloxy species and their analogs; and b) the exposing step is carried out such that silicon atoms belonging to the surface form chemical bonds with oxygen atoms of the silicon compound.
 5. The method of claim 1, wherein the silicon compound is an organo-H-silane compound that may be represented by the general formula HSiR'₁ R'₂ R'₃ wherein:a) each of the symbols R'₁ -R'₃ represents a substitutional species selected from the group consisting of: the hydrogen atom, the organic species and their analogs, and the organo-H-silane species and their analogs; and b) the exposing step is carried out such that silicon atoms belonging to the surface form chemical bonds with hydrogen atoms of the organo-H-silane compound.
 6. The method of claim 1, wherein the providing step comprises forming the article from molten glass, and the exposing step is carried out before the formed article is exposed to any substantial dose of water vapor.
 7. The method of claim 1, wherein the providing step comprises heating a silica-containing glass article to a temperature of at least about 600° C. but not more than the melting point of the article and the exposing step is carried out before the heated article is exposed to any substantial dose of water vapor.
 8. The method of claim 1, wherein the silicon compound is selected from the group consisting of the following compounds and their analogs:hexaMethyldiSiloxane; 1,1,3,3 tetraMethyldiSiloxane; 1,1,3,3 tetraVinyldiMethyldiSiloxane; 1,3 di(3-AminoPropyl)diMethyldiSiloxane; 1,3 di(3-MercaptoPropyl)diMethyldiSiloxane; 1,3 diBenzyltetraMethldiSiloxane; 1,3 diPhenyl 1,1,3,3 tetrakis di(MethylSiloxy)diSiloxane; 1,3 diPhenyltetraMethyldiSiloxane; 1,3 diVinyl 1,3 diPhenyl 1,3 diMethyldiSiloxane; 1,3 diVinyl tetraMethyldiSiloxane; hexaEthyldiSiloxane; tris-(triMethylSiloxy)Silane; the MethylHydrocycloSiloxanes; hexaMethylcyclotriSiloxane; isomers of tri(MethylHydro)cyclotriSiloxane; pentaMethylcyclotriSiloxane; 1,3,5,7 tetraVinyltetraMethylcyclotetraSiloxane; hexaEthylcyclotriSiloxane; EthylSilane; diMethylsilane; diEthylSilane; diEthylMethylSilane; the (MethylHydro)polySiloxanes; and 1,1,3,3,5 hexaMethyltriSiloxane.
 9. A method for manufacturing a fiber-optic cable, comprising the steps of:a) drawing a glass filament from an optical fiber preform, such that the filament, immediately after drawing, has a siloxane-terminated surface; and b) before exposing the siloxane-terminated surface to any substantial dose of water vapor, exposing the siloxane-terminated surface to at least one compound of silicon that has at least one Si--H group and/or at least one Si--O--Si group, leading to formation of reaction products chemically bound to the filament surface, wherein: c) the silicon-compound-exposing step is carried out such that: i. oxygen atoms belonging to the surface form chemical bonds with silicon atoms of the silicon compound; ii. silicon atoms belonging to-the surface form chemical bonds with hydrogen or oxygen atoms of the silicon compound; iii. no oxygen atom is simultaneously bound to a silicon atom and a carbon atom in any said reaction product: and iv. no oxygen atom becomes bound to a hydrogen atom as a result of the chemical reaction.
 10. The method of claim 9, further comprising, after the silicon-compound-exposing step, the steps of:a) coating the filament with a precursor material susceptible of polymerization; b) polymerizing the precursor material to form polymer jacket material; and c) before or during the polymerizing step, chemically reacting the precursor material with at least some of the reaction products, such that at least a portion of the polymer jacket material will be chemically bound to the filament surface.
 11. The method of claim 10, wherein:a) the silicon-compound-exposing step comprises exposing the siloxane-terminated surface to respective proportions of at least two distinct silicon compounds, each said compound capable of imparting a known, respective degree of adhesion between the filament and the polymer jacket material; and b) said respective proportions are selected to impart a predetermined, total degree of adhesion between the filament and the polymer jacket material. 